1. Field of the Invention
The present invention relates to a copying apparatus of the type in which an original to be copied is scanned and an image of the original is slit exposed on a photosensitive medium.
2. Description of the Prior Art
In an original scan type copying apparatus as mentioned above, the scanning of the original is carried out in various ways, for example, by reciprocally moving an original conveying means such as roller or belt together with the original or by reciprocally moving an original table on which the original has been placed or by moving optical elements such as mirrors or lenses along the original's fixed station. Usually, the original image is projected onto the photosensitive medium so as to make a copy from the original image only at the time of forward scanning. At the time of backward scanning of the original, the original image is not projected on the photosensitive medium. Therefore, the time necessary for the backward scanning is uselessly consumed and constitutes a loss of time. This is against the desire to increase the number of copies obtainable per unit of time.
To satisfy the above desire, many efforts have been made to provide a copying machine by which making a copy can be carried out not only during the forward scan time but also during the backward scan time. In fact, such a copying machine has already been disclosed in patent publications, for example, in German Pat. No. 2,527,381 and Japanese Pat. No. 17,380/1980. In the copying machines according to these prior arts there are used two roof mirrors for forward scanning and backward scanning of the original, respectively. These two roof mirrors are alternately interposed in and retracted from the optical path while keeping a proper relationship with the forward and backward scannings. As to the structure, these two roof mirrors are united together with the ridgeline of one roof mirror being orientated in the direction normal to that of the other roof mirror. With this arrangement, the images of the same original projected on the photosensitive medium at the time of forward scanning and at the time of backward scanning can be inverted 180.degree. relative to each other.
This prior art copying apparatus has, however, some drawbacks.
Since the two roof mirrors must be moved together at the time of reversal of the scanning direction, it takes relatively long time from the end of forward scanning to the start of backward scanning. This is because the weight of these two roof mirrors is relatively large and therefore a relatively long time is required to move the roof mirrors. Of course, this is against the desire to further increase the copying speed. Another drawback of the apparatus is found in the fact that the apparatus is apt to generate a large vibration and therefore to get in trouble very often due to the large weight of two roof mirrors which must be moved at every change of original scanning direction.